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Houseplants that Clean the Air

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The air in your home can be more polluted than air downtown at rush hour.

When we think of air pollution, we usually imagine a downtown street at rush hour, packed with cars emitting a gray and smelly cloud of chemicals. But the sad reality is that, in general, the air in our homes is more polluted then even rush hour air, especially during the winter when there is less air exchanged between the indoors and the outdoors. Indoor air can be, in fact, is 2 to 100 times more polluted than outdoor air.

Also, our homes are filled with objects that give off volatile organic compounds (VOCs): solvents, paintings, tapestries, carpets, furniture, clothing, glues, caulking, cosmetics, fireplaces, paper… and the list goes on and on. Among toxic VOCs commonly found in the average home are benzene, chloroform, formaldehyde, xylene, trichlorethylene, alcohol and acetone. If the problem is not as bad in summer, it’s because windows are often open and this ventilates the house. The situation is much worse in winter, especially in modern homes, which are better insulated than older buildings. Old buildings may be hard to heat, but at least they allow air to circulate more freely!

The effect on human health can be subtle – allergies, fatigue, depression, eye irritation, frequent colds – or more serious: polluted indoor air is believed to cause heart or lung problems, cancer, asthma and many others.

Plants to the Rescue

Plants – any plants! – will help keep the air clean!

However, plants can help clean up the air. They use same products that cause us so much harm – volatile organic compounds – as building blocks for their growth, breaking them down for use in building new cells. Thus, they filter the air of its impurities. In one closed chamber study, the air quality went from “toxic” to “excellent” within 15 minutes after a single fern was introduced! In addition to filtering the air of its pollutants, plants increase the air’s moisture level, another benefit for human health. Even more surprisingly, plants can also remove spores and bacteria present in the air, thereby helping reduce the risk of infection.

And do note it’s not just plants that clean the air, but also the microbes that live peacefully and invisibly on their roots. In fact, these microbes are even more efficient in cleaning the air than their host plants.

In the Workplace Too

A green workplace is a healthy workplace.

If houseplants can clean the air in our homes, they are just as useful in our offices and other workplaces. The most surprising thing is that, these days, you hear about more and more companies removing live plants from their buildings on the pretext that maintaining them is too expensive. Yet, studies show that office absenteeism diminishes markedly when plants are present and that employees in “greener” environments are more alert and efficient in all seasons. A wiser corporation would realize that maintaining plants costs relatively little compared to sick, absent and less effective employees!

All Plants are Air Cleaners!

Take your pick: just about any plant will clean the air.

The American space agency NASA has made many studies on the ability of plant to clean the air, originally because of their potential for use as living air filters in space stations and space colonies. Over the years some 100 plants were studied and all in fact proved to be very effective in cleaning the air. But these results have been largely misinterpreted by the media, which have touted lists of the “best plants for clean air” based on the few plants mentioned in the very first studies to appear. As a result, lots of people believe that spider plants, Boston ferns and peace lilies are more “efficient” air cleaners than other houseplants.

In fact, though, every plant tested did a good job of filtering the air and the differences between them were minor. The important thing to understand is not that one plant is better than another, but that plants well adapted to indoor conditions are more effective than plants that are barely able to survive there. If the spider plant, Boston fern and peace lily appeared to do so well on the first tests, it’s that they tend to grow particularly well under the environmental conditions of the average home. But whatever grows well in your home will be a good living air filter.

NASA’s List

Despite what I just wrote above, I know full well that many readers of this blog will insist on seeing “the list”, the one NASA produced of 50 houseplants that purify the air. (Many of you in fact will skip right over everything else and go straight to the list.)

The list is actually out-of-date (the studies date back to the 1980s) and in fact pretty much meaningless, as the plants were only tested for short periods. Some of the plants listed actually make horrible houseplants: gerberas and pot mums, for example, rarely live more than a few weeks indoors. But if people insist on believing that some plants are better than others, would repeating the list really be so harmful? After all, most of the plants the appear below really are decent houseplants and ought to be able to live in most homes. Besides, at least republishing the list does encourage readers to grow plants in their home and office and that’s what counts.

Here is NASA’s list of houseplants that purify the air, starting with those they found the most efficient:

That’s not an easy question to answer, because so many factors are involved: the degree of pollution, the season, the air circulation, how the home is heated, the lifestyle of the home’s occupant, the size of the room, the size and condition of the plants, the ability of the plant to adapt to the available conditions, etc. However authorities often recommend one medium-size plant* per 100 ft2 (9 m2)… and that would seem fairly accurate. That would mean about two or three plants per room. As air does circulate from one room to another, you could always keep fewer plants in some rooms and more in others.

*Medium size plant: one grown in a 10-inch (25 cm) pot.

And there you have it: grow the houseplants you want, but you do grow at least a few per room, both in your home and at your workplace: your health and that of your family and your colleagues depends on it.

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8 thoughts on “Houseplants that Clean the Air”

Great blog, Larry! It covers all the important and pertinent facts about plants’ ability to clean indoor air.

Plants aren’t all the same due to the wonderful adaptability of plants. So wouldn’t their air cleansing abilities be different?

For example, I was wondering how CAM plants fare as air cleansers? CAM plants are known for their different physiology. In their natural environment their open their stomata only during the night. CAM plants probably become C3 plants with indoor environmental conditions.

I don’t have an answer. I was wondering if you’ve come anything investigating the air-cleansing abilities of CAM plants? Fingers crossed.

I was just writing you about that when you wrote back. Yep, you did answer your own question! Remember too that most of the plants tested (in fact, all of them I suppose), were plants produced on mass in Florida greenhouses, where the studies were carried out. You’d probably have plenty more CAM plants on the list if you moved the study to Southern California!

Very few houseplants flower (most are grown for their foliage) and of those that do, almost none produce airborne pollen. I can’t think of a single exception to that, although there’s bound to be at least one. And in a windless atmosphere, any pollen so produced would probably just sink to the ground. I wouldn’t worry about pollen allergies if you’re growing houseplants.